Receiving system for high-frequency electrical oscillations



April 9, 1929. M. L. HARTMANN ET AL 1,708,573

RECEIVING SYSTEM FOR HIGH FREQUENCY ELECTRICAL OSCILLATIONS Filed Feb.21. 1925 VENTORS Patented Apr. 9, 1929.

UNITED STATES PATENT OFFICE.

MINER L. HARTM AN N AND MOB-ROW C. MILLER, OF NIAGARA FALLS, NEVT YORK,AS-

SIGNQRS TO THE CARBORUNDUM COMPANY, OF NIAGARA FALLS, NEEV YORK, A

CORPORATION OF PENNSYLVANIA.

RECEIVING SYSTEM FORHIGH-FREQUENCY ELECTRICAL OSCILLATIONS.

Application filed February direction, thereby rectifying the current.'All crystal rectifiers which have-"hereto fore been produced havedepended upon a very light touch between the two materials constitutingthe rectifier, and in either one or both of these there is constantlyexperienced the trouble of oxidation of the contact points. In practiceit has been found that the very best detectors or rectifiers of thistype last at best only a few months, particularly if used underconditions in which the voltage of the alternating high frequencycurrent is amplified before it reaches the detector.

We have discovered that by the use of our improved silicon carbidedetector, as described in our co-pending application, Serial No. 10,795filed of even date herewith, we are able to combine the advantages ofamplification or increasing the voltage of the incoming signals with arectifier which is not deleteriously afiected by high voltage, highfrequency impulses. V

In the drawings Figures 1 and 2 illustrate diagrammatically twodifferent types of receiving systems embodying our invention; and

Figure 3 is a View, partly broken out, of our cartridge tube type ofdetector.

Referring to the embodiment of our invention illustrated in Figure 1, 2designates a tuned antenna circuit for receiving the incoming signals,which areicarried to a radio frequency amplification unit consisting ofa 8-element vacuum tube, composed of the grid 4, thefilament 5 lightedby a battery 6, and the plate 7 connected through the primary 8 of thetransformer to a source of high direct current 9. By means of the actionof the audion tube 3 and the transformer 21, 1925. Serial No. 10,796.

primary 8, the voltage of the impulseis increased in the secondary coil10 of the phone circuit. This higher voltage current is then carriedthrough the rectifier composed of pure silicon carbide fragn'ient 11 andhardened steel plate 12 through the telephone 18, thus completing thesecondary or phone circuit.

While we have illustrated our invention in Figure 1 in connection withone stage of radio frequency amplification, it will be understood thattwo or more stages of amplification may be joined together and used incombinationwith our improved detector.

Figure 2 illustrates the use of our detector in combination with radiofrequency amplification preceding rectification and audio frequencyamplification after rectification. In this illustrated embodiment of ourinvention, 2 designates the tuned antenna circuit, 3 a g-element vacuumtube for amplification of the radio frequency impulses, 14: the radiofrequency transformer, 15 the audio transformer, 16 our silicon carbidedetector and 17 a 3-element vacuum tube for audio frequencyamplification.

lVe have shown in Figure 8 a preferred form of our silicon carbidedetector for use in receiving systems such as described above. Thisdetector and its method of manufacture will be briefly described, thesame being also described in more detail in our co-pending applicationabove referred to. It comprises asilicon carbide fragment 18 which hasbeen treated to remove all surface impurities therefrom. It is thencoated over approximately one-half of its surface, as by electroplatingor spraying, with a thin closely adhering film of conducting metal, suchas silver or copper. A second coating is then put on over the firstcoating consisting of non-oxidizing metal, such as an alloy of lead andtin. The coated fragment is then put in a mold and has a base 19 ofmetal, 'such as solder, cast about its coated portion. A hardened steelplate 20 is pressed against the silicon carbine fragment by a coilspring 21 with a pressure in the neighborhood of five pounds. The plate20 and base 19 are electrically connected to the binding posts 22 and 23carried by metal caps 24 at the ends of the dielectric tube 25. o havefound that a detector of this character has low electrical resistancenot only at the rectifying contact but also at the joint be= tween themetal conductor and the silicon carbide fragment. Actual tests made on arectifier of this type, develops the factrthat .j-it will rectifycurrents of the order of75 mill'iamperes and effectively withstand-thedestructive actionof currents ofthis value,

.1. whereby the rectifier is peculiarly adaptable to use in a radiocircuit wherein the relatively appended claim.

large currents of the radio frequency amplifying. side of the circuitare impressed on the rectifier.

It is to be understood that our invention is not limited to theembodiments thereof illustrated in Figures 1 and 2, but that it maybeour hands.

ceived oscillations, and a crystal detector con prising a crystal ofsilicon carbide and a contact element cooperating therewith,characterized by the factthat the crystal is free of those surfaceimpurities that form'on silicon carbide in its manufacture and'iscapable of rectifying-efficiently currents oi the order of 75milliamperes and wher'einthe pressure of the contact element is inexcess otoiie pound whereby it has a low contact resistance value,wherebysaid circuit secures efiicient rectification of the amplifiedsignal imp'ulseswhile maintaining their maximum effective value due tothe low contact resistance in the conducting direction of the crystal. a

In testimony whereof we have hereunto'set MINER L. "HARTMANN.

MORROW o. MILLER.

